The invention lies in the communications field and relates, more specifically, to a receiving method and a receiving device for use in mobile radio systems.
In cellular mobile radio systems, the geographic region which is to be supplied with radio communication is divided into cells. The reason for the cellular division is not only the attempt to supply the widest possible region (cellular network) with radio communications but also to provide for a high number of users (capacity) of the cellular network, which has a limited total transmission bandwidth, by means of so-called frequency reuse.
The principle of frequency reuse means that certain cells of the cellular network (which should be as far apart as possible) use the same frequency subband of the total transmission bandwidth. Each frequency subband, in turn, is subdivided into a number of user channels. The superimposition of signals coming from users who are active in the same channel in these cells having the same frequency subbands (xe2x80x9ccommon-channel cellsxe2x80x9d) is called cochannel interference.
In cellular mobile communication systems without band spreading (i.e. systems which do not use CDMA (code division multiple access) methods such as, for example, GSM (global system for mobile communications), cochannel interference is disadvantageous because it does not only impair the quality of service but, as a rule, also limits the capacity of the cellular network.
In Chapter 2 xe2x80x9cInterference suppression by joint demodulation of cochannel signalsxe2x80x9d, written by P. A. Ranta, M. Pukkila, of the book xe2x80x9cGSMxe2x80x94Evolution towards 3rd Generation Systemsxe2x80x9d by Z. Zvonar, P. Jung and K. Kammerlander (publisher), Boston, 1999, pages 153-86, it is proposed to use the method of joint detection, also referred to as xe2x80x9cJDxe2x80x9d, which, in the text which follows, is also referred to as multiuser detection for suppressing the cochannel interference.
In the article xe2x80x9cCombined Turbo Equalization and Turbo Decodingxe2x80x9d by D. Raphaeli and Y. Zarai, IEEE Communications Letters, Vol. 2, No. 4, 1998, pages 107-09, an iterative receiving method is described. An MAP (maximum a posteriori) symbol estimator is used for adaptive channel estimation and a turbo decoder following the MAP symbol estimator is used for decoding. The MAP symbol estimator and the turbo decoder are arranged in a feedback-loop and perform an iterative single-user equalization.
In the document xe2x80x9cCombined Multiuser Reception and Channel Decoding for TDMA Cellular Systemsxe2x80x9d by M. C. Valenti et al., Ottawa, Canada, May 18-21, 1998, New York, N.Y.: IEEE, US, Vol. CONF. 48, May 18, 1998 (1998-05-18), a multiuser receiving method is described, wherein an iterative equalization is performed by means of a loop consisting of a multiuser data detector and a channel decoder.
European patent application EP 0 866 568 A1 describes a multiuser receiving method wherein a number of receiving antennas are used for signal reception. This provides for directionally selective detection of the received data.
It is accordingly an object of the invention to provide a reception method and a receiver for mobile radio applications, which overcome the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which create an efficient receiving method and an efficient receiving device for a mobile radio system which does not use a CDMA multiple access method. In particular, it should be possible to achieve coverage for a high number of users, i.e. capacity.
With the foregoing and other objects in view there is provided, in accordance with the invention, a receiving method for mobile radio applications, which comprises the following steps:
receiving a given user data signal (i.e., a signal transmitted by a certain user or a signal intended for a certain receiving user) and at least one further user data signal within a same frequency band;
source decoding the received signal and generating an extrinsic information item;
iteratively equalizing the given user data signal and the further user data signal with an adaptive multiuser data
detector and with a multiuser channel decoder connected via a feedback path to the adaptive multiuser data detector;
and thereby effecting a noise reduction in the iteratively equalized given user data signal by taking into consideration the further user data signal, and utilizing the extrinsic information item during channel decoding.
In accordance with another feature of the invention, turbo decoding is performed in the multiuser channel decoding.
With the above and other objects in view there is also provided, in accordance with the invention, a receiving device for mobile radio communications, comprising:
a radio-frequency stage for receiving a given user data signal (i.e., a signal transmitted by a certain user or a signal intended for a certain receiving user) and at least one further user data signal located within the same frequency band as the given user signal; and
an iterative equalizer connected to the radio-frequency stage and adapted to equalize the given user data signal and the further user data signal, the iterative equalizer including an adaptive multiuser data detector and a multiuser channel decoder connected in a feedback path to the adaptive multiuser data detector, and the iterative equalizer being configured to utilize in a channel decoding operatin an extrinsic information item generated during source decoding.
In accordance with a further feature of the invention, the adaptive multiuser data detector is configured to perform coherent data detection.
In accordance with a concomitant feature of the invention, the adaptive multiuser data detector is configured to perform, with respect to a user data signal, a channel estimation for a plurality of data signals provided by a plurality of spatially separate receiving sensors.
By combining the principle of multiuser detection with an iterative equalization, two complementary techniques for improving the signal-to-noise ratio are combined. While the multiuser detection is based on considering a part of the cochannel interference as useful signal, i.e. detecting it selectively and then eliminating it from the certain user data signal which is actually of interest (this is possible because the cochannel interference is deterministic in its nature), the iterative equalization is based on the principle of achieving error reduction by utilizing decoded information during the data detection. The latter is done by way of repeated feedback of reliability information, obtained during the multiuser decoding, into the multiuser data detector. The iterative equalization for error reduction is perfoxmed both on the certain user data signal, i.e. the xe2x80x9cactualxe2x80x9d useful signal, and on the other user data signal, i.e. the cochannel interference signal components treated as useful signal during JD as a result of which these two principles (multiuser detection and iterative equalization) mutually influence and support one another. To improve the results obtained during the iterative equalization an extrinsic information item generated during a source decoding is also used.
In accordance with an added feature of the invention, coherent data detection is performed in the iterative multiuser equalization. In other words, during the iterative equalization, a coherent data detection is preferably performed. A coherent data detection further increases the noise immunity which can be achieved by means of the receiving method according to the invention (or, respectively, the noise immunity of the receiving device according to the invention).
In accordance with an additional feature of the invention, a plurality of data signals received from spatially separate receiving sensors are taken into consideration in the adaptive multiuser data detection. The spatial separation of the receiving sensors has the effect that the individual data signals are transmitted via different transmission channels having (more or less, depending on the distance of the receiving sensors) different transmission characteristics, i.e. having different impulse responses. Taking into consideration a number of such data signals from spatially separate receiving sensors for a user data signal makes it possible to further increase the fault tolerance of the data detection.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in reception method and receiveer for mobile radiotelephone applications, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.